Photopolymerizable composition and use thereof

ABSTRACT

A photopolymerizable composition comprising a polymerizable compound and a photopolymerization initiator, wherein the polymerizable compound is characterized by comprising (a) a bifunctional (meth)acrylic acid (thio)ester compound containing a sulfur atom in the molecule and (b) at least one of a (meth)acrylic acid ester compound represented by the general formula (1) or a bifunctional (meth)acrylic acid ester compound having a urethane linkage:  
                 
         wherein R 1  and R 2  are each independently a hydrogen atom or a methyl group; R 3  and R 4  are each independently an alkyl group, an aralkyl group, an aryl group or a halogen atom; m and n are each an integer of 0 to 2; X 1  is an alkylidene group having 1 to 3 carbon atoms; and Y 1  and Y 2  are each independently a poly(oxyalkylene) group with the proviso that at least one of Y 1  and Y 2  is a poly(oxyalkylene) group having a hydroxy group.

TECHNICAL FIELD

The present invention relates to a photopolymerizable composition inwhich polymerization and curing can be realized within a short period oftime by irradiating light such as ultraviolet rays and the like, andoptical parts which can be obtained by polymerizing thephotopolymerizable composition. More particularly, it relates to opticalparts including lens fields such as a spectacle lens for opticalcorrection, a pickup lens in information recording devices such as CD,DVD and the like, a plastic lens for cameras such as a digital cameraand the like, a contact lens and the like, and sealing material fieldsin a light emitting element and the like.

BACKGROUND ART

As an inorganic glass is excellent in its transparency and has excellentgeneral properties such that optical anisotropy is low, it has been usedin many fields as a transparent optical material. However, it hasdrawbacks in that it is easily broken due to its heavy weight and hasbad productivity in processing optical parts. As a result, a transparentorganic polymer material (optical resin) has been actively underdevelopment as a material for replacing the inorganic glass. Recently,high functionality and high quality in optical resins have beenpromoted. Optical parts obtained by molding and processing of theseoptical resins have further come into wide use in, for example, lensfields such as a spectacle lens for optical correction, a pickup lens ininformation recording devices such as CD, DVD and the like, a plasticlens for cameras such as a digital camera and the like, and sealingmaterial fields in a light emitting element and the like.

One of the most important and fundamental properties as an optical resinis transparency. Up to now, as an optical resin having excellenttransparency, there are known resins, for example, polymethylmethacrylate (PMMA), polycarbonate (BPA-PC), polystyrene (PS), methylmethacrylate-styrene copolymer (MS), styrene-acrylonitrile copolymer(SAN), poly(4-methyl-1-pentene) (TPX), polycycloolefin (COP), diethyleneglycol bisallylcarbonate polymer (DAC), polythiourethane (PTU), andepoxy compounds such as 2,2-bis (4-hydroxyphenyl)propane (commonlycalled bisphenol A) type epoxy compound, an alicyclic epoxy compound andthe like, and an epoxy resin which can be obtained using an acidanhydride compound as a curing agent.

Among these optical resins, polymethyl methacrylate (PMMA) is widelyused as one of representative optical resins as it is superior in itstransparency and has characteristics such that optical anisotropy isrelatively low (low double refractive index), and molding and weatherresistance are good. However, there are drawbacks in that its refractiveindex (nd) is low, i.e., 1.49 and the water absorption coefficient ishigh.

In the same manner, polycarbonate (BPA-PC), one of the representativeoptical resins, can be obtained by the polycondensation reaction of2,2-bis(4-hydroxyphenyl)propane (hereinafter referred to as bisphenol Awhat is commonly called) and a carbonate compound (for example, carbonylchloride, diphenylcarbonate or the like), having characteristics suchthat transparency, heat resistance and impact resistance are excellent,and the refractive index (nd=1.59) is relatively high. As a result, itis widely used for optical purposes including an optical disk plate forinformation recording. However, it has drawbacks in that the chromaticaberration (dispersion of refractive index), double refractive index arerelatively high and melting viscosity is high, thus making formingrather difficult. Needless to say, improvement of performance andcharacteristics is being made to overcome these drawbacks.

Diethylene glycol bisallylcarbonate polymer (DAC) is a thermosettingresin of a crosslinked high molecular structure to be obtained bycasting radical polymerization of a monomer, i.e., diethylene glycolbisallylcarbonate. It has characteristics such that transparency andheat resistance are excellent, and the chromatic aberration is very low.Due to such characteristics, it is used the most for a general-purposeplastic spectacle lens for optical correction. However, there aredrawbacks in that its refractive index is low (nd=1.50) and its impactresistance is rather inferior.

Polythiourethane (PTU) is a thermosetting resin of a crosslinked highmolecular structure to be obtained by the reaction between adiisocyanate compound and a polythiol compound. It is an extremelyexcellent optical resin having characteristics such that itstransparency and impact resistance are excellent, the refractive indexis high (nd ≧1.6), and the chromatic aberration is relatively low. Atpresent, it is used the most for the purpose of a high-quality plasticspectacle lens for optical correction in which the thickness is thin andits weight is light. However, there is room for further improvement onlyin the production process for lens requiring long time (1 to 3 days) forthermal polymerization molding.

In order to solve these problems and to produce optical parts such asoptical lenses and the like with high productivity, there has beenproposed a method to polymerize and mold a compound having radicalpolymerization ability (hereinafter referred to as polymerizablecompound) for obtaining an aiming molded product within a short periodof time in the presence of a compound (photopolymerization initiator)for initiating radical polymerization by irradiating light such asultraviolet rays and the like (for example, JP92-180911A, JP88-207632,JP86-194401 or the like).

As a representative example of the polymerizable compound used for thephotopolymerization, a (meth)acrylic acid ester compound is, forexample, used. However, there have been proposed a (meth)acrylic acidester compound or a (meth)acrylic (thio) ester compound or the likehaving a particular structure containing a bromine atom or a sulfur atomin order to obtain much higher refractive index and Abbe number.According to these methods, polymerization can be realized within ashort period of time. However, considering a balance in the generalproperties such as transparency, dyeing property, optical properties(for example, refractive index, Abbe number or the like), thermalproperties (for example, heat distortion temperature or the like),mechanical properties (for example, impact resistance, flexuralstrength, adhesion or the like) and the like, it is difficult to mentionthat the thus-obtained cured product (resin) is sufficiently satisfyingas optical parts for spectacle lens materials or sealing materials forlight emitting elements and the like.

As the polymerizable compound containing a sulfur atom, there has beenproposed that a cured product of a bifunctional or multifunctional(meth)acrylic acid thioester compound to be derived from a thiolcompound such as bis(2-mercapto ethyl) sulfide and the like is useful asa transparent resin having high refractive index (JP95-91262B,JP94-25232B and the like). JP94-2523B has described polymerization andcuring by photopolymerization of the (meth)acrylic acid thioestercompounds without presenting any concrete Examples. When optical partsare actually manufactured by photopolymerization using the (meth)acrylicacid thioester compound as described in the above patent publication,difference in composition of the polymerizable composition andphotopolymerization conditions results in difference in physicalproperties of resin cured product to be obtained, so it is difficult tomention that they have physical properties for actual use in many cases.

Already known optical resins have excellent characteristics as describedabove, but, according to the present state, each of them has alsodrawbacks to overcome. Under these circumstances, it is required todevelop optical resins such as spectacle lens materials or sealingmaterials for light emitting elements such that polymerization andforming can be performed by photopolymerization within a short period oftime, in which transparency and optical properties (high refractiveindex and Abbe number) of the thus-obtained cured product or opticalparts are excellent, and thermal properties and mechanical propertiesare good.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide optical resins in whichproblems of optical resins used for optical parts as described above areto be solved. More particularly, it is to provide a photopolymerizablecomposition in which polymerization and forming can be performed byphotopolymerization within a short period of time, and a balance is goodfrom the viewpoint of general properties such as transparency, opticalproperties (for example, refractive index, Abbe number and the like),thermal properties (for example, heat distortion temperature and thelike), mechanical properties (for example, impact resistance, flexuralstrength, adhesion and the like), dyeing property and the like, andoptical parts to be obtained by polymerizing the polymerizable compound.

As a result of extensive review, the present inventors have found aphotopolymerizable composition comprising a polymerizable compound and aphotopolymerization initiator, wherein the polymerizable compound ischaracterized by using (a) a bifunctional (meth)acrylic acid (thio)estercompound containing a sulfur atom in the molecule and (b) at least oneof a (meth)acrylic acid ester compound represented by the generalformula (1) or a bifunctional (meth)acrylic acid ester compound having aurethane linkage together:

-   -   wherein R₁ and R₂ are each independently a hydrogen atom or a        methyl group; R₃ and R₄ are each independently an alkyl group,        an aralkyl group, an aryl group or a halogen atom; m and n are        each an integer of 0 to 2; X, is an alkylidene group having 1 to        3 carbon atoms; and Y₁ and Y₂ are each independently a        poly(oxyalkylene) group with the proviso that at least one of Y₁        and Y₂ is a poly(oxyalkylene) group having a hydroxy group,    -   and in which, due to this, polymerization and forming can be        performed by photopolymerization within a short period of time,        a balance is good from the viewpoint of general properties such        as transparency, optical properties (refractive index and Abbe        number), heat resistance, mechanical properties (impact        resistance, flexural strength and adhesion), dyeing property and        the like; and optical parts which can be obtained by        polymerizing the polymerizable composition, thus completing the        present invention.

Namely, the present invention relates to a photopolymerizablecomposition comprising a polymerizable compound and aphotopolymerization initiator, wherein the polymerizable compound ischaracterized by comprising (a) a bifunctional (meth)acrylic acid(thio)ester compound containing a sulfur atom in the molecule and (b) atleast one of a (meth)acrylic acid ester compound represented by thegeneral formula (1) or a bifunctional (meth)acrylic acid ester compoundhaving a urethane linkage:

-   -   wherein R₁ and R₂ are each independently a hydrogen atom or a        methyl group; R₃ and R₄ are each independently an alkyl group,        an aralkyl group, an aryl group or a halogen atom; m and n are        each an integer of 0 to 2; X₁ is an alkylidene group having 1 to        3 carbon atoms; and Y₁ and Y₂ are each independently a        poly(oxyalkylene) group with the proviso that at least one of Y₁        and Y₂ is a poly(oxyalkylene) group having a hydroxy group,    -   and a photopolymerizable compound further comprising (C)        polythiols.

Furthermore, it relates to a cured product to be obtained bypolymerizing the polymerizable composition, optical parts made of thecured product and a light emitting element made by sealing with thecured product.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a main portion in an opticalsemiconductor equipment manufactured in Examples 24 and 25.

FIG. 2 is a cross sectional view of a main portion in an opticalsemiconductor equipment manufactured in Example 26.

DESCRIPTION OF REFERENCE NUMBERS

-   1 Sealing resin layer (formed using the sealing material of the    present invention)-   2 Leadframe-   3 Leadframe-   4 Mounting section (Mounting member)-   5 Outer sealing resin layer (formed using an epoxy type sealing    material)-   6 Conductive paste-   7 Light emitting element-   7 a Compound semiconductor substrate-   7 b n-type electrode-   7 c p-type electrode-   8 wire

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described in more detail below.

A photopolymerizable composition according to the present inventioncomprising a polymerizable compound and a photopolymerization initiatoris characterized in that the polymerizable compound comprises (a) abifunctional (meth)acrylic acid (thio)ester compound containing a sulfuratom in the molecule and (b) at least one of a (meth)acrylic acid estercompound represented by the general formula (1) or a bifunctional(meth)acrylic acid ester compound having a urethane linkage:

-   -   wherein R₁ and R₂ are each independently a hydrogen atom or a        methyl group; R₃ and R₄ are each independently an alkyl group,        an aralkyl group, an aryl group or a halogen atom; m and n are        each an integer of 0 to 2; X₁ is an alkylidene group having 1 to        3 carbon atoms; and Y₁ and Y₂ are each independently a        poly(oxyalkylene) group with the proviso that at least one of Y₁        and Y₂ is a poly(oxyalkylene) group having a hydroxy group,    -   and polythiols are further contained.

In the photopolymerizable composition, a polymerizable compound isformed into a transparent resin by being polymerized and cured with theaction of a compound which initiates polymerization by generating theradical by applying the active energy line such as light or the like(hereinafter referred to as photopolymerization initiator).

(a) A bifunctional (meth)acrylic acid (thio)ester compound containing asulfur atom in the molecule used in the present invention is describedbelow.

Any known bifunctional (meth)acrylic acid (thio)ester compoundcontaining a sulfur atom in the molecule can be used for (a) abifunctional (meth)acrylic acid (thio)ester compound containing a sulfuratom in the molecule used in the present invention. However, a desirableformula is described in the following compound group represented by thegeneral formula (3):

-   -   wherein R₆ and R₇ are each independently a hydrogen atom or an        alkyl group; Z₁ and Z₂ are each independently an oxygen atom or        a sulfur atom; A is a linking group with the proviso that A        contains at least one sulfur atom in case Z₁ and Z₂ are all        oxygen atoms.

A more desirable formula is represented by the general formula (2):

-   -   wherein R₅ is a chain alkylene group having at least one or more        sulfur atoms in the group or a linking group as shown below; R₆        and R₇ are each independently a hydrogen atom or an alkyl group;        Z₁ and Z₂ are each independently an oxygen atom or a sulfur atom        with the proviso that any one of Z₁ and Z₂ is a sulfur atom in        case R₁ is the linking group represented by the following:    -   wherein R₁₂ and R₁₃ are each independently an alkyl group, an        aralkyl group, an aryl group or a halogen atom; and q and r are        each an integer of 0 to 2.

More preferably, in the above general formula (2), at least one of Z₁and Z₂ is a sulfur atom. In the above general formula (2), a compoundrepresented by the general formula (4) is the most preferable, in whichboth Z₁ and Z₂ are sulfur atoms:

-   -   wherein R₅ is a chain alkylene group having at least one or more        sulfur atoms in the group or a linking group represented by the        following; and R₆ and R₇ are each independently a hydrogen atom        or an alkyl group:    -   wherein R₁₂ and R₁₃ are each independently an alkyl group, an        aralkyl group, an aryl group or a halogen atom; and q and r are        each an integer of 0 to 2.

Incidentally, a plurality of R₁₂ substituents and a plurality of R₁₃substituents each may be the same or different.

As the most preferable (a) bifunctional (meth)acrylic acid (thio)estercompound containing a sulfur atom in the molecule, there can bementioned, for example, compounds such as bis(2-acryloylthioethyl)sulfide, 1,8-bisacryloylthio-3,6-dithiaoctane,1,11-bisacryloylthio-3,6,9-trithiaundecane and the like.

According to the present invention, as (a) a bifunctional (meth)acrylicacid (thio)ester compound containing a sulfur atom in the molecule,bis(2-acryloylthioethyl) sulfide is a particularly preferable compoundin consideration of a balance in general physical properties (opticalproperties, thermal properties, mechanical properties and the like)required for optical parts.

An acrylic acid thioester compound represented by the general formula(4) is properly produced by various known (thio)esterification methodsincluding the following representative examples

-   -   (1) a method (the method described in JP98-67736A and the like)        of reacting a dithiol compound represented by the general        formula (5) with an acyl halide (for example, acyl chloride,        acyl bromide and the like) of an halopropionic acid (for        example, 3-chloropropionic acid, 3-bromopropionic acid,        3-chloro-2-methylpropionic acid, 3-bromo-2-methylpropionic acid        and the like) to produce a halopropionic acid thioester compound        represented by the general formula (6), and then performing        acrylic acid thio-esterification by dehydrohalogenation (for        example, dehydrochlorination, dehydrobromination and the like);        and    -   (2) a method of acting such manipulation as dropping an acyl        halide of (meth)acrylic acid into a dithiol compound represented        by the general formula (5) in the presence of a base under        stirring, or a method of performing transesterification between        a dithiol compound represented by the general formula (5) and a        (meth)acrylic acid ester derivative [for example, (meth)acrylic        acid alkylester such as (meth)acrylic acid methylester,        (meth)acrylic acid ethylester, (meth)acrylic acid butylester and        the like] in the presence of a catalyst (acid catalyst or base        catalyst) [for example, a method described in Experimental        Chemistry (Chemical Society of Japan), pages 19, 471 to 482        (Year 1957), Journal of Organic Chemistry, vol. 45, page 5346        (Year 1980), European Polymer Journal, vol. 19, page 399        (Year 1983) and the like]:        HS—R₅—SH  (5)    -   wherein R₅ is a chain alkylene group having at least one or more        sulfur atoms in the group or a linking group represented by the        following:    -   wherein R₁₂ and R₁₃ are each independently an alkyl group, an        aralkyl group and aryl group or a halogen atom; and q and r are        each an integer of 0 to 2;    -   wherein E₁ and E₂ are each a chlorine atom or a bromine atom;        and R₅ is the same one as described above.

An acrylic acid thioester compound represented by the general formula(4) according to the present invention is isolated throughpost-treatment according to the known manipulation and treatment method(for example, neutralization, solvent extraction, washing, separation,removal of solvent and the like) after the above reaction is terminated.Furthermore, an acrylic acid thioester compound represented by thegeneral formula (4) is separated and purified by known methods (forexample, chromatography, treatment by means of an activated carbon orvarious absorbents) and isolated as a monomer compound having muchhigher purity and of high quality as desired.

Also, it is desirable for a solution to have a small amount ofimpurities (for example, insoluble substance, insoluble particle, dust,foreign substance and the like) by filtering to have high transparency.For example, the above impurities can be removed by means of a method offiltering an acrylic acid thioester compound (liquid) represented by thegeneral formula (4) using a filter in a clean room and the like.

Next, (b) a (meth)acrylic acid ester compound represented by the generalformula (1) and a bifunctional (meth)acrylic acid ester compound havinga urethane linkage are described in detail below.

(b) Any of a (meth)acrylic acid ester compound represented by thegeneral formula (1) or a bifunctional (meth)acrylic acid ester compoundhaving a urethane linkage may be used together with (a) a bifunctional(meth)acrylic acid (thio)ester compound containing a sulfur atom in themolecule, thus obtaining an intended effect. However, a better balancedcured product can be obtained with a (meth)acrylic acid ester compoundrepresented by the general formula (1) so that it is desirable to use itrather than a bifunctional (meth)acrylic acid ester compound having aurethane linkage.

In the general formula (1), R₁ and R₂ are each independently a hydrogenatom or a methyl group.

R₃ and R₄ groups are each independently an alkyl group, an aralkylgroup, an aryl group or a halogen atom. R₃ and R₄ groups are preferablyan alkyl group having 1 to 4 carbon atoms, an aralkyl group having 6 to20 carbon atoms, an aryl group having 6 to 20 carbon atoms, a chlorineatom or a bromine atom, and more preferably a methyl group, an ethylgroup, benzyl group, a phenyl group or a bromine atom. Incidentally, aplurality of R₃ substituents and a plurality of R₄ substituents each maybe the same or different.

In the general formula (1), n and m are each an integer of 0 to 2. n andm are preferably 0 or 1, and an integer of 0 is particularly preferable.

In the general formula (1), X₁ represents an alkylidene group having 1to 3 carbon atoms. The X₁ group is preferably a methylidene group, anethylidene group, a propylidene group or an isopropylidene group, andmore preferably a methylidene group and an isopropylidene group.Considering the intended effect of the present invention, as the X₁group, an isopropylidene group is particularly preferable.

In the general formula (1), Y₁ and Y₂ are each independently apoly(oxyalkylene) group with the proviso that at least one of Y₁ and Y₂is a poly(oxyalkylene) group having a hydroxy group. Considering theintended effect of the present invention, ay one of Y₁ and Y₂ is morepreferably a poly(oxyalkylene) group having a hydroxy group. The Y₁ andY₂ groups are most preferably the group represented by the followingformula.

A (meth)acrylic acid ester compound represented by the general formula(1) is preferably a compound represented by the formula (1-a), (1-b) or(1-c):

-   -   wherein R₁ to R₄, m, n, X₁, Y₁ and Y₂ are the same as those        described above.

It is more preferably a compound represented by the formula (1-a) or(1-b) and further preferably a compound represented by the formula(1-a).

As a compound represented by the general formula (1) according to thepresent invention, there can be mentioned, for example,2,2-bis[4-(3-acryloyloxy-2-hydroxypropyloxy)phenyl]propane,2,2-bis[2-(3-acryloyloxy-2-hydroxypropyloxy)phenyl] propane,2-[2-(3-acryloyloxy-2-hydroxypropyloxy)phenyl]-2-[4-(3-acryloyloxy-2-hydroxypropyloxy)phenyl]propane,2,2-bis[4-(3-methacryloyloxy-2-hydroxypropyloxy)phenyl] propane,2,2-bis[2-(3-methacryloyloxy-2-hydroxypropyloxy)phenyl]propane,2-[2-(3-methacryloyloxy-2-hydroxypropyloxy)phenyl]-2-[4-(3-methacryloyloxy-2-hydroxypropyloxy)phenyl]propane,2,2-bis[4-(3-methacryloyloxy-2-hydroxypropyloxy)-3-methylphenyl]propane,2,2-bis[4-(3-methacryloyloxy-2-hydroxypropyloxy)-3-benzylphenyl]propane,2,2-bis[4-(3-methacryloyloxy-2-hydroxypropyloxy)-3-phenylphenyl]propane,2,2-bis[4-(3-methacryloyloxy-2-hydroxypropyloxy)-3,5-dibromophenyl]propane,2-[4-(2-acryloyloxyethyloxy)phenyl]-2-[4-(3-acryloyloxy-2-hydroxypropyloxy)phenyl]propane,2-[3-(2-acryloyloxyethyloxy)phenyl]-2-[4-(3-acryloyloxy-2-hydroxypropyloxy)phenyl]propane,2-[4-(2-acryloyloxyethyloxy)phenyl]-2-[3-(3-acryloyloxy-2-hydroxypropyloxy)phenyl]propane,2-[4-(2-methacryloylethyloxy)phenyl]-2-[4-(3-methacryloyloxy-2-hydroxypropyloxy)phenyl]propane,2-[3-(2 -methacryloylethyloxy)phenyl]-2-[4-(3-methacryloyloxy-2-hydroxypropyloxy)phenyl]propane,2-[4-(2-methacryloyloxyethyloxy)phenyl]-2-[3-(3-methacryloyloxy-2-hydroxypropyloxy)phenyl]propaneand the like. However, it is not restricted thereto.

Considering the intended effect of the present invention, any one of Y₁and Y₂ is preferably a poly(oxyalkylene) group having a hydroxy group asdescribed above and a compound represented by the formula (1-a-i) isparticularly preferable:

-   -   wherein R₁ and R₂ are the same as those described above.

(b) A bifunctional (meth)acrylic acid ester having a urethane linkage tobe used in the present invention is represented by the following generalformula (7):

-   -   wherein R₈ to R₁₁ are each independently a hydrogen atom or a        methyl group; and B represents the following linking group.

As a bifunctional (meth)acrylic acid ester compound having a urethanelinkage, the following linking group B in the above formula representedby the following is preferable as much higher transparency can beobtained.

Next, (c) polythiols are explained below. In the present invention, apolythiol type represents a compound having two or more thiol groups(mercapto group) in the molecule. Specific examples are listed below;however the present invention is not restricted thereto1,2-ethanedithiol, 1,3-propanedithiol, 1,6-hexanedithiol,1,12-dodecanedithiol, mercaptomethyl sulfide, 2-mercaptoethyl sulfide,3-mercaptopropyl sulfide, 6-mercaptohexyl sulfide,1,2-bis-2-mercaptoethyl thioethane, 1,2-bis-3-mercaptopropyl thioethane,1,3-bis-2-mercaptoethyl thiopropane, 1,4-bis-2-mercaptoethyl thiobutane,1,6-bis-2-mercaptoethyl thiohexane, bis-2-(2-mercaptoethylthio)ethylsulfide, 2-mercaptoethyl ether, 3-mercaptopropyl ether, 6-mercaptohexylether, 1,4-cyclohexanedithiol, bis-2-mercaptoethoxy methane,1,2-bis-2-mercaptoethoxy ethane, bis-2-(2-mercaptoethoxy)ethylether,4-mercaptomethyl-3,6-dithia-1,8-octanedithiol,5-mercapto-3,7-dithia-1,9-nonanedithiol, 1,4-benzenedithiol,1,3-benzenedithiol, 1,2-benzenedithiol, 4-t-butyl-1,2-benzenedithiol,1,2-bis(mercaptomethylene)benzene, 1,3-bis(mercaptomethylene)benzene,1,4-bis(mercaptomethylene)benzene, 1,2-bis(mercaptoethylene)benzene,1,3-bis(mercaptoethylene)benzene, 1,4-bis(mercaptoethylene)benzene,1,2-bis(mercaptomethylenethio)benzene,1,3-bis(mercaptomethylenethio)benzene,1,4-bis(mercaptomethylenethio)benzene,1,2-bis(2-mercaptoethylenethio)benzene,1,3-bis(2-mercaptoethylenethio)benzene,1,4-bis(2-mercaptoethylenethio)benzene, 1,2-bis(2-mercaptoethylenethiomethylene)benzene, 1,3-bis(2-mercaptoethylene thiomethylene)benzene,1,4-bis(2-mercaptoethylene thiomethylene)benzene,1,2-bis(mercaptomethyleneoxy)benzene,1,3-bis(mercaptomethyleneoxy)benzene,1,4-bis(mercaptomethyleneoxy)benzene,1,2-bis(2-mercaptoethyleneoxy)benzene,1,3-bis(2-mercaptoethyleneoxy)benzene,1,4-bis(2-mercaptoethyleneoxy)benzene, 4,4′-thio dithio phenol,4,4′-biphenyldithiol, 1,3,5-trimercaptobenzene, trimercaptoethylisocyanurate, pentaerythritol tetrathioglycolate, pentaerythritoltrithioglycolate, pentaerythritol dithioglycolate, pentaerythritoltetramercaptopropionate, pentaerythritol trimercaptopropionate,pentaerythritol dimercaptopropionate, trimethylolpropanetrithioglycolate, trimethylolpropane dithioglycolate, trimethylolpropanetrimercaptopropionate, trimethylolpropane dimercaptopropionate, andmercaptopropyl isocyanurate.

Next, the photopolymerizable composition of the present invention isexplained in detail.

The photopolymerizable composition of the present invention comprises apolymerizable compound and a photopolymerization initiator as essentialcomponents, wherein the polymerizable compound comprises (a) abifunctional (meth)acrylic acid (thio)ester compound containing a sulfuratom in the molecule (hereinafter (a) component) and (b) at least one ofa (meth)acrylic acid ester compound represented by the general formula(1) or a bifunctional (meth)acrylic acid ester compound having aurethane linkage (hereinafter (b) component) and, if necessary, furthercomprises (c) polythiols (hereinafter (c) component):

Each of these (a), (b) and (c) components may use the aforementionedcompounds singly or in combination. Also, it is natural that (b) a(meth)acrylic acid ester compound represented by a plurality the generalformulae (1) and a bifunctional (meth)acrylic acid ester compound havinga plurality of urethane linkage may be used together.

The ratio of the (a) component to the total weight of the (a) componentand (b) component (hereinafter total weight α) contained in thephotopolymerizable composition of the present invention is usually 5 to95 weight %, preferably 10 to 90 weight %, more preferably 20 to 80weight %, and most preferably 30 to 70 weight %.

In the same way, the ratio of the (b) component to the total weight α isusually 95 to 5 weight %, preferably 90 to 10 weight %, more preferably80 to 20 weight % and most preferably 70 to 30 weight %.

Incidentally, in order to achieve the intended effect of the presentinvention, the ratio of the total weight α occupied in the total weightof the polymerizable compound contained in the photopolymerizablecomposition of the present invention is 50 weight % or more, preferably60 weight % or more, more preferably 70 weight % or more, and furtherpreferably 80 weight % or more.

Furthermore, the ratio of the (c) component to the total weight of thephotopolymerizable composition is 0 to 30 weight %, preferably 0 to 25weight %, and more preferably 0 to 20 weight %.

The photopolymerizable composition of the present invention contains aphotopolymerization initiator as an essential component, whereas thephotopolymerization initiator to be used may be compounds generating theradical by the action of light such as ultraviolet rays. As thephotopolymerization initiator, various known compounds are used.

As the photopolymerization initiator, there can be mentioned, forexample, carbonyl compounds such as benzophenon, 4-methylbenzophenon,4,4′-dichlorobenzophenon, 2,4,6-trimethylbenzophenon, o-benzoyl benzoicacid methylester, 4-phenylbenzophenon, 4-(4-methylphenylthio)benzophenon, 3,3-dimethyl-4-methylbenzophenon,4-(1-3-acryloyl-1,4-7,10,13-pentaoxatridecyl)benzophenon,3,3′,4,4′-tetra(tert-butylperoxycarbonyl)benzophenon,4-benzoyl-N,N,N-methyl benzene metanaminium chloride,2-hydroxy-3-(4-benzoylphenoxy)-N,N, N-trimethyl-1-propanaminiumchloride, 4-benzoyl-N,N-dimethyl-N-[2-(1-oxo-2-propanoxy) ethyl]benzenemetanaminium bromide,4-benzoyl-N,N-dimethyl-N-[2-(1-oxo-2-prophenyloxy)ethyl]benzenemetanaminium bromide, 2-isopropyl thioxanthone, 4-isopropylthioxanthone, 2,4-dimethyl thioxanthone, 2,4-diethyl thioxanthone,2,4-diisopropyl thioxanthone, 2,4-dichlorothioxanthone,1-chloro-4-propoxythioxanthone,2-hydroxy-3-(3,4-dimethyl-9-oxo-9H-thioxanthone-2-yloxy)-N,N,N-trimethyl-1-propanaminiumchloride, 2-benzoylmethylene-3-methylnaphto(1,2-d)thiazoline and thelike; dicarbonyl compounds such as benzyl,1,7,7-trimethyl-bicyclo[2,2,1]haptane-2,3-dion (usually calledcamphorquinone), 2-methylanthraquinone, 2-ethylanthraquinone,2-tert-butylanthraquinone, 1-chloroanthraquinone, 2-amylanthraquinone,9,10-phenanthrenequinone, α-oxobenzeneacetic acid methylester and thelike; acetophenone type compounds such as acetophenone,2-hydroxy-2-methyl-1-phenylpropane-1-on,1-(4-isopropylphenyl)-2-hydroxy-2-methylpropane-1-on,1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methylpropane-1-on,1-hydroxycyclohexylphenylketone, dimethoxyacetophenone,diethoxyacetophenone, 2,2-dimethoxy-1,2-diphenylethane-1-on,2,2-diethoxy-1,2-diphenylethane-1-on, 1,1-dichloroacetophenone,N,N-dimethylaminoacetophenone,2-methyl-1-(4-methylthiophenyl)-2-morphorino propane-1-on,2-benzyl-2-dimethylamino-1-(4-morphorino phenyl)butane-1-on,1-phenyl-1,2-propanedion-2-(o-ethoxycarbonyl)oxime,3,6-bis(2-methyl-2-morphorino propanoyl)-9-butylcarbazole and the like;benzoine ether type compounds such as benzoine, benzoine methylether,benzoine ethylether, benzoine isopropylether, benzoine-n-butylether,benzoine isobutylether and the like; aryl phosphineoxide type compoundssuch as 2,4,6-trimethylbenzoyl diphenylphosphineoxide, bis(2,6-dichlorebenzoyl)-(4-n-propylphenyl)phosphineoxide and the like; aminocarbonylcompounds such as 4-dimethylamino benzoic acid methylester,4-dimethylmino benzoic acid ethylester, 4-dimethylanimo benzoicacid-n-butoxyethylester, 4-dimethylamino benzoic acid isoamylester,benzoic acid-2-dimethylamino ethylester, 4,4′-bisdimethylaminobenzophenon (Michler's ketone), 4,4′-bisdiethylamino benzophenon,2,5′-bis(4-dimethylaminobenzal)cyclopentanone and the like; halogencompounds such as 2,2,2-trichloro-1-(4′-tert-butylphenyl)ethane-1-on,2,2-dichloro-1-(4-phenoxyphenyl)ethane-1-on, α,α,α-tribromomethylphenylsulfon, 2,4,6-tris(trichloromethyl)triazine,2,4-trichloromethyl-6-(4-methoxyphenyl)triazine,2,4-trichloromethyl-6-(4-methoxystyryl)triazine,2,4-trichloromethyl-6-piperonyl-triazine,(2,4-trichloromethyl-6-(3,4-methylenedioxyphenyl)-triazine),2,4-trichloromethyl-6-(4-methoxynaphthyl)-triazine,2,4-trichloromethyl-6-[2-(5-methylfuryl)ethylidine]triazine,2,4-trichloromethyl-6-[2-furyl ethylidine]triazine and the like; knowncompounds such as 9-phenylacridine,2,2′-bis(o-chlorophenyl)-4,4′,5,5′-tetraphenyl-1,2-biimidazole,2,2-azobis(2-aminopropane)dihydrochloride,2,2,-azobis[2-(imidazoline-2-yl)propane]dihydrochloride,η-5-2-4-(cyclopentadienyl)(1,2,3,4,5,6,η)-(methylethyl)-benzene]iron(II)hexa fluorophosphate,bis(5-cyclopentadienyl)bis[2,6-difluoro-3-(1H-pil-1-yl)phenyl]titaniumand the like.

These photopolymerization initiators may be used singly or incombination of two or more kinds. Furthermore, a known photosensitizermay also be used together as desired.

The content of the photopolymerization initiator to the 100 weight partsof the polymerizable compound contained in the photopolymerizablecomposition is usually 0.001 to 5 weight parts, preferably 0.002 to 3weight parts, more preferably 0.005 to 2 weight parts, and furtherpreferably 0.01 to 2 weight parts.

In case the photopolymerizable composition of the present invention isto be polymerized and cured, light and heat may be used together forsuch polymerization and curing as desired. In this case, in addition tothe aforementioned photopolymerization initiator, a compound generatingthe radical by the action of heat (hereinafter referred to as thermalpolymerization initiator) is used together.

In these compounds, various known compounds are used as a thermalpolymerization initiator, which include, for example, ketone peroxidessuch as methylethylketone peroxide, cyclohexanone peroxide,methylcyclohexanone peroxide, methylacetoacetate peroxide, acetylacetoneperoxide and the like; peroxy ketals such as1,1-bis(tert-hexylperoxy)3,3,5-trimethylcyclohexane,1,1-bis(tert-hexylperoxy)cyclohexane,1,1-bis(tert-butylperoxy)3,3,5-trimethylcyclohexane,di-tert-butylperoxy-2-methylcyclohexane and the like; hydroperoxidessuch as P-methane hydroperoxide, diisopropylbenzene hydroperoxide,1,1,3,3-tetramethylbutyl hydroperoxide, cumene hydroperoxide, tert-hexylhydroperoxide, tert-butyl hydroperoxide and the like; dialkyl peroxidessuch as α,α′-bis(tert-butylperoxy)diisopropylbenzene, dicumyl peroxide,2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, tert-butyl-cumyl peroxide,di-tert-butyl peroxide, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexyn-3and the like; diacyl peroxides such as isobutyl peroxide,3,3,5-trimethylhexanoyl peroxide and the like; diacyl peroxides such asoctanoyl peroxide, lauroyl peroxide, stearoyl peroxide, succinic acidperoxide, benzoyl peroxide and the like; peroxydicarbonates such asdi-n-propylperoxydicarbonate, diisopropylperoxydicarbonate,bis(4-tert-butylcyclohexyl)peroxydicarbonate, di-2-ethoxyethylperoxydicarbonate, di-2-ethylhexyl peroxydicarbonate, di-2-ethylhexylperoxydicarbonate, di-3-methoxybutylperoxydicarbonate,di(3-methyl-3-methoxybutyl)peroxydicarbonate and the like; peroxy esterssuch as α,α-′bis(neodecanoylperoxy)diisopropylbenzene, cumyl peroxydecanoate, 1,1,3,3-tetramethylbutyl peroxyneodecanoate,1-cyclohexyl-1-methylethyl peroxyneodecanoate, tert-hexylperoxyneodecanoate, tert-butyl peroxyneodecanoate, tert-hexyl peroxypivalate, tert-butyl peroxy pivalate,1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, 2,5-dimethyl-2,5-bis(2-ethylhexanoylperoxy)hexane,1-cyclohexyl-1-methylethylperoxy-2-ethylhexanoate,tert-hexylperoxy-2-ethylhexanoate, tert-butylperoxy-2-ethylhexanoate(usually called per-butyl-O), tert-butylperoxy-isobutylate,tert-hexylperoxy-isopropyl monocarbonate, tert-butylperoxy-maleic acid,tert-butylperoxy-3,3,5-trimethylhexanoate, tert-butylperoxy-laurate,2,5-dimethyl-2,5-bis(m-tolylperoxy)hexane, tert-butylperoxy-isopropylmonocarbonate, tert-butylperoxy-2-ethylhexyl monocarbonate,tert-hexylperoxy-benzoate, 2,5-dimethyl-2,5-bis(benzoylperoxy)hexane,tert-butylperoxy-acetate, tert-butylperoxy-m-tolylbenzoate,tert-butylperoxy-benzoate, bis(tert-butylperoxy)isophthalate and thelike; organic peroxides such as tert-butylperoxy allyl monocarbonate,tert-butyl trimethyl cyril peroxide,3,3′,4,4′-tetra(tert-butylperoxycarbonyl)benzophenon,2,3-dimethyl-2,3-diphenylbutane and the like; or azo compounds such asazobisisobutyronitrile and the like. However, the present invention isnot restricted thereto.

These thermal polymerization initiators may be used singly or incombination of two or more kinds.

The amount of the thermal polymerization initiator to the 100 weightparts of the polymerizable compound is usually 0.001 to 5 weight parts,preferably 0.002 to 3 weight parts, more preferably 0.005 to 2 weightparts, and further preferably 0.01 to 2 weight parts.

Furthermore, in the photopolymerizable composition of the presentinvention, other polymerizable compounds (light or thermal polymerizablemonomer, oligomer and the like) in addition to each of theabove-mentioned (a), (b) and (c) components may be used as apolymerizable compound within the range of not damaging an intendedeffect as needed.

Various known polymerizable compounds (polymerizable monomer,polymerizable oligomer or the like) are used for the other polymerizablecompounds, which include, for example, known polymerizable monomers suchas monofunctional (meth)acrylates such as methyl(meth)acrylate,butyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, ethyl carbitol(meth)acrylate, lauryl (meth)acrylate, phenoxyethyl (meth)acrylate,nonylphenoxyethyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl(meth)acrylate, dicyclopentenyl (meth)acrylate, isobornyl(meth)acrylate, N-n-butyl-O-(meth)acryloyloxyethyl carbamate,acryloylmorpholine, trifluoroethyl (meth)acrylate, tribromo benzyl(meth)acrylate, perfuluorooctylethyl (meth)acrylate and the like;silicon-containing (meth)acrylates such as (meth)acryloyloxy propyltris(methoxy)silane and the like; alkylene glycol di(meth)acrylates such asethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate,neopentyl glycol di(meth)acrylate, 1,6-hexane diol di(meth)acrylate andthe like; polyalkylene glycol di(meth)acrylates such as triethyleneglycol di(meth)acrylate, tripropylene glycol di(meth)acrylate,polyethylene glycol di(meth)acrylate, polypropylene glycoldi(meth)acrylate and the like; multifunctional (meth)acrylates such astrimethylolpropane tri(meth)acrylate, dipentaerythritol pentaacrylate,pentaerythritol triacrylate, pentaerythritol tetraacrylate,ditrimethylol tetraacrylate, dipentaerythritol hexaacrylate an the like;epoxy (meth)acrylates such as ethylene glycol diglycidylether(meth)acrylate, propylene glycol diglycidylether (meth)acrylate,phenolglycidylether (meth)acrylate, resorcin diglycidylether(meth)acrylate, 4,4′-bishydroxy phenyl sulfide diglycidylether(meth)acrylate and the like; epoxy (meth)acrylates such as reactants ofepoxy compounds (for example, phenolnovolak type epoxy resin, cresolnovolak type epoxy resin, bisphenol type epoxy resin, biphenol typeepoxy resin, tris(2,3-epoxypropyl)isocyanurate and the like) andacrylate or methacrylate; monofunctional vinyl compounds such asvinylbenzene, divinylbenzen, N-vinylpyrrolidone, N-vinylcaprolctam andthe like; known polymerizable monomers such as allyl group-containingcompound (for example, ethylene glycol diallylcarbonate, trimelliticacid triallyl ester, triallyl isocyanurate and the like), or variousknown polymerizable oligomers such as (poly)epoxy(meth)acrylate,(poly)ester(meth)acrylate, polyether(meth)acrylate and the like.

These polymerizable compounds may be used singly or in combination oftwo or more kinds.

In order to achieve an intended effect of the present invention, theratio of other polymerizable compounds occupied in the total weight ofthe polymerizable compound contained in the photopolymerizablecomposition of the present invention is usually less than 50 weight %,preferably less than 40 weight %, more preferably less than 30 weight %,and further preferably less than 20 weight %.

The photopolymerizable composition of the present invention is notparticularly restricted relative to its state. However, it is preferablya liquid at room temperature (25° C.) in consideration of its handling,workability and the like when using.

The viscosity of the photopolymerizable composition of the presentinvention at room temperature (25° C.) is preferably 100 to 10000000 cps(mPa·s), more preferably 100 to 100000 cps (mPa·s) and furtherpreferably 200 to 100000 cps (mPa·s).

The liquid refractive index of the photopolymerizable composition of thepresent invention at room temperature (25° C.) is preferably more than1.53 and more preferably more than 1.55.

The refractive index of the cured product to be obtained by polymerizingthe photopolymerizable composition of the present invention at roomtemperature (25° C.) is preferably more than 1.56, more preferably morethan 1.57 and further preferably more than 1.58.

As the method for producing the photopolymerizable composition of thepresent invention, there can be mentioned, for example, a method foradding, if necessary, (c) polythiols or said other polymerizablecompound(s) (hereinafter referred to as component B) to a mixture(hereinafter referred to as component A) of (a) a bifunctional(meth)acrylic (thio)ester compound containing a sulfur atom in themolecule and (b) a (meth)acrylic acid ester compound represented by thegeneral formula (1) or a bifunctional (meth)acrylic acid ester compoundhaving a urethane linkage, and then adding the polymerization initiatorand finally mixing/dissolving them.

Before photopolymerizing the photopolymerizable composition, it isdesirable to filter and eliminate impurities such as insolublesubstance, foreign substance, insoluble particles or the like. Then, itis desirable to perform photopolymerization for this photopolymerizablecomposition after sufficiently degassing under reduced pressure.Photopolymerization without sufficiently degassing is not desirable asbubbles might be mixed in the cured product.

As a light source used for photopolymerization, a chemical lamp, a xenonlamp, a low-pressure mercury lamp, a high-pressure mercury lamp, a metalhalide lamp and the like can be used.

The time of irradiating light for photopolymerization is also influencedby such conditions as light intensity of the light source to be used.However, it usually takes several seconds to several ten of minutes.

Furthermore, when thermal polymerization is performed together,polymerization temperature is influenced by the polymerizationconditions such as kinds of the polymerization initiator so that it isnot restricted. However, polymerization temperature is usually 25 to200° C. and preferably 50 to 170° C.

Various known additives can also be added to the photopolymerizablecomposition of the present invention within the range of not damagingthe intended effect of the present invention as needed, which include ananti-oxidant, a light (ultraviolet rays, visible rays, infrared rays andthe like) absorbent, a filler (for example, inorganic fillers such astalc, silica, alumina, barium sulfate, magnesium oxide, organic filleror the like), a pigment, a dye, a coupling agent, a mold release agentand the like.

The cured product of the present invention and optical parts made of thecured product are obtained by photopolymerization and curing of thephotopolymerizable composition. At this time, several known methods canbe applied. However, as a representative method, there can be mentioned,for example, a casting polymerization using the polymerization reactionwhich is initiated by the radical generated by irradiation of lightafter the photopolymerizable composition obtained as described above isintroduced to the mold.

As a molding method for an optical lens, as described above, there hasbeen proposed a method to obtain a lens by performing castingpolymerization by means of light or the like (for example, JP85-135901A,JP98-67736A, JP98-130250A and the like). Namely, such a method isproperly performed such that the photopolymerizable composition producedby the above-mentioned method is introduced to the mold after degassingby means of a proper method as needed and usually light-irradiated forpolymerization.

This mold consists of, for example, two pieces of mirror surface-groundmolds via a gasket made of polyethylene, ethylene vinyl acetatecopolymer, poly vinyl chloride and the like. As a mold, there can bementioned, combined molds such as glass and glass, glass and plasticplate, glass and metal plate, and the like. Furthermore, as the gasket,the above-mentioned soft thermoplastic resin (polyethylene, ethyl vinylacetate copolymer, poly vinyl chloride and the like) is used and furthertwo pieces of molds may be fixed with a polyester adhesive tape or thelike. In addition, a known method such as the mold release process maybe performed for the mold.

Since photopolymerization, the cured product or optical parts to beobtained by releasing from the mold may be subject to annealing processfor the purpose of eliminating internal stress, distortion or the like.

Furthermore, for purposes of anti-reflection, high hardness grant, wearresistance improvement, anti-fogging property grant or fashionabilitygrant, various known physical or chemical processes such as surfacepolishing, antistatic process, hard coat process, non-reflective coatprocess, anti-reflective process, dyeing process, photochromic process(for example, photochromic lens process and the like) and the like maybe performed.

As a molding method for a plate-shape molded product, there can bementioned, for example, conventional known methods such as a method forinjecting the photopolymerizable composition of the present inventioninto the cavity of a plate mold, polymerizing them by light radicalpolymerization, and, if necessary, performing post-thermal treatment(JP83-130450A, JP83-137150A, JP87-280008A and the like); a method forperforming photopolymerization in the both-sided glass mold(JP85-202557A); a method for performing thermal polymerization of theliquid resin under pressure after vacuum casting or the liquid injectionwas completed (JP85-203414A), and the like.

As the optical parts of the present invention, there are concretelymentioned, for example, a spectacle lens for optical correction, aliquid crystal projector or a fresnel lens for projector television, alenticular lens, pickup lenses of information recording devices such asCD, DVD and the like, a contact lens, various plastic lenses such as alens for cameras including a digital camera, a sealing material of alight emitting element or an optical waveguide, optical adhesivematerials to be used for junction of an optical lens and an opticalwaveguide, an anti-reflection film to be used for an optical lens,transparent coating or transparent substrate to be used for a liquidcrystal display-related member (substrate, light guiding plate, film,sheet and the like).

As a method for sealing the light emitting element by polymerization andcuring of the photopolymerizable composition of the present invention,various known methods are properly performed. However, as representativeexamples, there can be mentioned a casting molding method such ascasting or the like, a transfer molding method and the like.

Sealing materials for the light emitting element of the presentinvention can be used together with other known sealing materials forthe light emitting element (for example, epoxy resin type sealingmaterial, silicon resin type sealing material or the like). Namely,there can be mentioned, for example, a method which comprises sealing alight emitting element having the refractive index of 2 or more with asealing material for the light emitting element having the highrefractive index of the present invention to form a sealing resin layer,and then further sealing the outer side thereof with the aforementionedknown sealing material having the relatively low refractive index toform the sealing resin layer.

It takes about several minutes to tens of minutes required forpolymerization (curing) and molding in the cured product which can beobtained by photopolymerization of the photopolymerizable composition ofthe present invention and optical parts which are made of the curedproduct. As compared to thermosetting optical resins represented by theconventional polydiethylene glycol diallylcarbonate andpolythiourethane, one of characteristics of the cured product andoptical parts is that such polymerization (curing) and molding can beperformed within a short period of time and productivity of the moldedproduct is high.

The cured product and optical parts of the present invention have goodtransparency and excellent optical properties (high refractive index andhigh Abbe number) along with thermal properties and mechanicalproperties, which are, for example, used as optical lenses such as aspectacle lens for optical correction and the like or sealing materialsof the light emitting element properly. The photopolymerizablecomposition of the present invention is also used for purposes ofhologram recording material, dental supplies or the like as thephotopolymerizable material which can obtain high refractive index, inaddition to the aforementioned optical parts.

EXAMPLES

The present invention is described specifically below by way ofProduction Examples and Examples. However, the present invention is notrestricted to these Examples.

Production Example 1 Production of a Compound (MESDA) Represented by theFormula (4-1) of the Present Invention

A mixed solution of 231.48 g (1.50 mol) of bis(2-mercaptoethyl) sulfideand 1000 g of toluene was heated at 110° C. and thereinto was dropped457.09 g (3.60 mol) of 3-chloropropano yl chloride over 2 hours. Whenall was dropped, the reaction mixture was further stirred for another 7hours at 110° C., while by-product hydrogen chloride was removed out ofthe reaction system under nitrogen stream. Then no raw material existingin the high performance liquid chromatography (hereinafter referred toas HPLC analysis) was confirmed, and the reaction solution was cooleddown to room temperature. The reaction mixture was discharged in 5000 gof 5% sodium bicarbonate aqueous solution (corresponding to 3.0 mol assodium bicarbonate), thereto was further added 1000 g of toluene, andthe reaction product was extracted. An organic layer was repeatedlywashed using the ion exchange water until a drainage layer wasneutralized. Then, the organic layer was taken out by separation, andthen toluene was removed at 30° C. under reduced pressure andconcentrated to obtain 476.54 g of a coarse composition of a colorlessand transparent liquid, i.e.,bis[2-(3-chloropropionylthio)ethyl]sulfide. The purity of the coarsecomposition was 95% (HPLC analysis by the internal standard method) andthe yield was 90% (purity conversion).

476.54 g of the thus-obtained bis[2-(3-chloropropionylthio)ethyl]sulfide (1.35 mol for a target product with the converted purity)was dissolved in 2000 g of acetone to obtain a solution. Thereinto weredropped 323.80 g of triethyl amine (3.20 mol) at 5° C. over an hour.When the triethyl amine was all dropped, the reaction mixture wasfurther reacted while being stirred for another 2 hours, and then no rawmaterial existing in the HPLC was confirmed and returned to roomtemperature (25° C.). Thereto were added 7000 g of hexane and 7000 g ofpure water to stir at 25° C. and extract. 10% hydrochloric acid wasadded to the hexane solution in the organic layer at room temperature,washing and separation were repeated until no chlorine ion was detected,and then solution separation was performed to take out the organiclayer. 450 mg of 4-methoxyphenol, i.e., a polymerization inhibitor wasadded thereto, hexane was removed at 35° C. under reduced pressure andconcentrated to obtain 348.04 g of a colorless and transparent liquid,i.e., bis(2-acryloylthio ethyl) sulfide (MESDA). The yield was 84%[yield from bis(2-mercaptoethy) sulfide, purity conversion value] andthe purity was 95% (HPLC analysis by the internal standard method).

The liquid refractive index nd at room temperature (25° C.) of thecompound was 1.610.

Production Example 2 Production of a Compound (IPDI-HPMA) Represented bythe Formula (7-1) of the Present Invention

A 1-liter reaction container was provided with a stirrer, a thermometer,a drying tube and a dropping funnel 200 g (0.9 mol) of isophoronediisocyanate (IPDI), 0.2 g of dibutyltin dilaurate as a catalyst, and0.13 g of 2,6-di-t-butyl-4-methylphenol (BHT) as a polymerizationinhibitor were fed thereinto and heated at 70° C. The solutionmaintained its temperature at 70° C. while 259.4 g (1.8 mol) of2-hydroxy propyl methacrylate (HPMA) was dropped over 2 hours using thedropping funnel, and then it was further stirred at the same temperaturefor 8 hours. The reaction termination was determined such that thereaction was terminated at the time when more than 97% of an isocyanategroup was consumed in measurement of the isocyanate equivalent by thetitration method. The reaction solution was used as it was in productionof the photopolymerizable composition.

Production Example 3 Production of a Compound (XDI-HEMA) Represented bythe Formula (7-2) of the Present Invention

A 1-liter reaction container was provided with a stirrer, a thermometer,a drying tube and a dropping funnel. 169.4 g (0.9 mol) of m-xylylenediisocyanate (XDI), 0.2 g of dibutyltin dilaurate as a catalyst, and0.13 g of 2,6-di-t-butyl-4-methylphenol (BHT) as a polymerizationinhibitor were fed thereinto and heated at 70° C. The solutionmaintained its temperature at 70° C. while 234.3 g (1.8 mol) of2-hydroxy ethyl methacrylate (HEMA) was dropped over 2 hours using thedropping funnel, and then it was further stirred at the same temperaturefor 8 hours. The reaction termination was determined such that thereaction was terminated at the time when more than 97% of an isocyanategroup was consumed in measurement of the isocyanate equivalent by thetitration method. The reaction solution was used as it was in productionof the photopolymerizable composition.

Example 1 Production of Photopolymerizable Composition of the PresentInvention

50.0 g of MESDA produced according to Production Example 1, and 50.0 gof 2,2 -bis(4-hydroxyphenyl)propane diglycidyl methacrylate (Bis-GMA)having methacrylic acid ester compound of the following formula (1-1) asa main component was weighed and mixed in 300 ml eggplant type brownglass flask. 0.07 g of diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide(TMDPO) (0.07 weight % to the total weight of the polymerizablecompound) as a photopolymerization initiator was added thereto, mixed,stirred and dissolved. Then, the mixture was slowly stirred at roomtemperature under reduced pressure for sufficiently degassing until nobubble was recognized, pressurized, filtered using a filer manufacturedby Teflon to obtain 100.0 g of a colorless and transparent liquid, i.e.,the photopolymerizable composition.

Example 2 Production of Photopolymerizable Composition of the PresentInvention

The photopolymerizable composition was produced in the same manner as inExample 1, except that 67.0 g of MESDA, 17.0 g of Bis-GMA and 16.0 g oftetraethylene glycol dimethacrylate (TMGDMA) were used instead of 50.0 gof MESDA and 50.0 g of Bis-GMA in Example 1.

Example 3 Production of Photopolymerizable Composition of the PresentInvention

The photopolymerizable composition was produced in the same manner as inExample 1, except that 0.07 g (0.07 weight % to the total weight of thepolymerizable compound) of 2-hydroxy-2-methyl-1-phenylpropane-1-on(Darocure-1173) was used instead of 0.07 g ofdiphenyl(2,4,6-trimethylbenzoyl)phosphine oxide as a polymerizationinitiator in Example 1.

Example 4 Production of Photopolymerizable Composition of the PresentInvention

The photopolymerizable composition was produced in the same manner as inExample 1, except that 75.0 g of MESDA and 25.0 g of IPDI-HPMA producedin Example 2 were used instead of 50.0 g of MESDA and 50.0 g of Bis-GMAin Example 1.

Example 5 Production of Photopolymerizable Composition of the PresentInvention

The photopolymerizable composition was produced in the same manner as inExample 1, except that 60.0 g of MESDA and 40.0 g of XDI-HEMA producedin Example 3 were used instead of 50.0 g of MESDA and 50.0 g of Bis-GMA.

Example 6 Production of Photopolymerizable Composition of the PresentInvention

The photopolymerizable composition was produced in the same manner as inExample 1, except that 50.0 g of MESDA, 25.0 g of Bis-GMA and 25.0 g ofIPDI-HPMA were used instead of 50.0 g of MESDA and 50.0 g of Bis-GMA.

Example 7 Production of Photopolymerizable Composition of the PresentInvention

The photopolymerizable composition was produced in the same manner as inExample 1, except that 50.0 g of MESDA, 40.0 g of Bis-GMA and 10.0 g ofmercapto ethyl sulfide (MES) were used instead of 50.0 g of MESDA and50.0 g of Bis-GMA in Example 1.

Example 8 Production of Photopolymerizable Composition of the PresentInvention

The photopolymerizable composition was produced in the same manner as inExample 1, except that 70.0 g of MESDA, 20.0 g of IPDI-HPMA and 10.0 gof pentaerythritol tetramercapto propionate (PEMP) were used instead of50.0 g of MESDA and 50.0 g of Bis-GMA in Example 1.

Example 9 Production of Photopolymerizable Composition of the PresentInvention

The photopolymerizable composition was produced in the same manner as inExample 1, except that 50.0 g of MESDA, 20.0 g of IPDI-HPMA, 25.0 g ofBis-GMA and 5.0 g of MES were used instead of 50.0 g of MESDA and 50.0 gof Bis-GMA in Example 1.

The following products were obtained and used for the polymerizablecompound and photopolymerization initiator used in production of thepolymerizable composition in the above Examples.

-   -   2,2-bis(4-hydroxyphenyl)propane diglycidyl methacrylate; epoxy        ester 3000M, Bis-GMA (a product of Kyoeisha Chemical Co., Ltd.)    -   Tetraethylene glycol dimethacrylate; NK ester 4G, TEGDMA (a        product of Shin-Nakamura Chemical Co., Ltd.)    -   Mercaptoethyl sulfide; MES (a product of Maruzen Chemical Co.,        Ltd.)    -   Pentaerythritol tetramercapto propionate; PEMP (a product of        Aldrich Co.)    -   Diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide; TMDPO (a        product of Aldrich Co.)    -   2-hydroxy-2-methyl-1-phenylpropane-1-on; Darocure-1173 (a        product of Ciba Specialty Chemicals Inc.)

Production of a Cured Product by Curing the PhotopolymerizableComposition of the Present Invention

The physical properties of a cured product or optical parts (lens)produced in the following Examples or Comparative Examples wereevaluated in the following methods.

Appearance: Hue, transparency, optical distortion, striae were confirmedvisually or using a microscope.

Permeability: A visible and ultraviolet spectrum of a cured product inthe shape of a board having a length of 50 mm, width of 20 mm, thicknessof 1 mm was measured to obtain the permeability (T %) at 400 nm.

Refractive index and Abbe Number: These were measured at 20° C. using aPulfrich refractometer.

Specific gravity: It was measured using DENSIMETER D-1 (a product ofToyo Seiki Seisaku-sho, Ltd.).

Heat resistance: A glass transition temperature (Tg) was measured fromthe displacement point of TMA curve of the cured product by the needlesoaking method using the Thermomechanical Analysis Method (TMA Method).

Dyeing property: The cured product was dipped in a dye solution of 5 g/lat 90° C. for 10 minutes and the dyeing property was visuallydetermined. Evaluation criteria were (⊚; extremely excellent, ◯;excellent, Δ; not bad and x: bad. Dyes used were MLP-Red-2, MLP-Blue-2,MLP-Gold-Yellow-2 (products of Mitsui Toatsu Dye).

Example 10 Production of a Cured Product by Photopolymerization of thePhotopolymerizable Composition of the Present Invention

The photopolymerizable composition produced in Example 1 was fed intothe center of a mold manufactured using a silicon rubber as a spacerbetween two pieces of mirror surface-finished glass plates. Using ametal halide lamp (120 W/cm), ultraviolet rays were irradiated from bothtop and bottom sides of the glass mold for 180 seconds to performpolymerization. When polymerization was terminated, the mold was slowlycooled and a cured product was taken out of the mold. The cured productwas heat-treated (annealed) at 120° C. for an hour, and then thethus-obtained cured product was examined. As a result, the cured productwas colorless and transparent, and no optical distortion or striae wasconfirmed. The permeability at 400 nm was 88%, the refractive index (ne)of the cured product was 1.604, Abbe number (ve) was 35.8, and thespecific gravity was 1.37. A glass transition temperature (Tg) was 139°C. The dyeing property was very good.

Example 11 Production of a Cured Product by Photopolymerization of thePhotopolymerizable Composition of the Present Invention

The photopolymerizable composition produced in Example 2 was fed intothe center of a mold manufactured using a silicon rubber as a spacerbetween two pieces of mirror surface-finished glass plates. Using ametal halide lamp (120 W/cm), ultraviolet rays were irradiated from bothtop and bottom sides of the glass mold for 180 seconds to performpolymerization. When polymerization was terminated, the mold was slowlycooled and a cured product was taken out from the mold. The curedproduct was heat-treated (annealed) at 100° C. for 2 hours, and then thethus-obtained cured product was examined. As a result, the cured productwas colorless and transparent, and no optical distortion or striae wasconfirmed. The permeability at 400 nm was 88%.

The refractive index (ne) of the cured product was 1.614, Abbe number(ve) was 37.9, and the specific gravity was 1.37. A glass transitiontemperature (Tg) was 122° C. The dyeing property was very good.

Examples 12 to 18 Production of a Cured Product by Photopolymerizationof the Photopolymerizable Composition of the Present Invention

The cured product was obtained by conducting polymerization in the samemanner as in Example 11, except that the photopolymerizable compositionsproduced in Examples 3 to 9 were used instead of the photopolymerizablecomposition produced in Example 1. TABLE 1 Glass PolymerizablePhotopolymerization Refractive Abbe Transition Light Ex- CompoundInitiator Index Number Temperature Permeability Distortion Dyeing ample(weight parts) (weight parts) Color (ne) (ve) (° C.) (%) StriaeProperty^(#) 12 MESDA (50) Darocure-1173 Colorless 1.604 35.8 139 88 No⊚ Bis-GMA (50) (0.07) Transparent 13 MESDA (75) TMDPO (0.07) Colorless1.606 37.5 138 89 No ◯ IPDI-HPMA (25) Transparent 14 MESDA (60) TMDPO(0.07) Colorless 1.610 36.1 137 88 No ◯ XDI-HEMA (40) Transparent 15MESDA (50) TMDPO (0.07) Colorless 1.596 36.5 138 89 No ⊚ Bis-GMA (25)Transparent IPDI-HPMA (25) 16 MESDA (50) TMDPO (0.07) Colorless 1.61136.3   100< 88 No ⊚ Bis-GMA (40) Transparent MES (10) 17 MESDA (70)TMDPO (0.07) Colorless 1.609 37.3   100< 88 No ◯ IPDI-HPMA (20)Transparent TEMP (10) 18 MESDA (50) TMDPO (0.07) Colorless 1.593 36.5  100< 88 No ⊚ Bis-GMA (25) Transparent IPDI-HPMA (20) MES (5)^(#)Evaluation criteria of the dyeing property⊚; extremely excellent,◯; excellent,Δ; not bad, andX; bad.

Example 19 Production of a Lens

After sufficiently degassing the photopolymerizable composition producedin Example 1 under reduced pressure, the composition was poured into amold frame (adjusted to a minus lens shape) comprising a glass mold andtape. Using a metal halide lamp (120 W/cm), ultraviolet rays wereirradiated from both top and bottom sides of the mold frame for 60seconds, the composition was heated at 80° C. for an hour and anannealing process was conducted. When polymerization was terminated, themold was cooled down to room temperature to obtain a colorless andtransparent minus lens having a diameter of 30 mm and a center thicknessof 1.3 mm. The thus-obtained lens was colorless and transparent, andoptically uniform without any optical distortion or striae beingobserved. The refractive index (ne) of the lens was 1.604, and Abbenumber (ve) was 35.8. Heat resistance (heat distortion temperature) ofthe lens according to the present invention, and impact resistance weregood, the dyeing property of a known disperse dye used for dyeing of aspectacle lens for optical correction was extremely excellent.

Example 20 Production of a Lens

After sufficiently degassing the photopolymerizable composition producedin Example 4 under reduced pressure, the composition was fed into a moldframe (adjusted to a minus lens shape) comprising a glass mold and tape.Using a metal halide lamp (120 W/cm), ultraviolet rays were irradiatedfrom both top and bottom sides of the mold frame for 60 seconds, thecomposition was heated at 100° C. for an hour and an annealing processwas conducted. When polymerization was terminated, the mold was cooleddown to room temperature to obtain a colorless and transparent minuslens having a diameter of 30 mm and a center thickness of 1.3 mm. Thethus-obtained lens was colorless and transparent, and optically uniformwithout any optical distortion or striae being observed. The refractiveindex (ne) of the lens was 1.606, and Abbe number (ve) was 37.5. Heatresistance (heat distortion temperature) of the lens according to thepresent invention, and impact resistance were good, the dyeing propertyof a known disperse dye used for dyeing of a spectacle lens for opticalcorrection was excellent.

Example 21 Production of a Lens

After sufficiently degassing the photopolymerizable composition producedin Example 7 under reduced pressure, the composition was fed into a moldframe (adjusted to a minus lens shape) comprising a glass mold and tape.Using a metal halide lamp (120 W/cm), ultraviolet rays were irradiatedfrom both top and bottom sides of the mold frame for 120 seconds, thecomposition was heated at 80° C. for an hour and an annealing processwas conducted. When polymerization was terminated, the mold was cooleddown to room temperature to obtain a colorless and transparent minuslens having a diameter of 30 mm and a center thickness of 1.3 mm. Thethus-obtained lens was colorless and transparent, and optically uniformwithout any optical distortion or striae being observed. The refractiveindex (ne) of the lens was 1.611, and Abbe number (ve) was 36.3. Heatresistance (heat distortion temperature) of the lens according to thepresent invention, and impact resistance were good, the dyeing propertyof a known disperse dye used for dyeing of a spectacle lens for opticalcorrection was extremely excellent.

Example 22 Production of the Photopolymerizable Composition for Sealinga Light Emitting Element of the Present Invention

The photopolymerizable composition for sealing the light emittingelement was produced in the same manner as in Example 1, except that0.20 g (0.20 weight % to the total weight of the polymerizable compound)of Darocure-1173 as a photopolymerization initiator was used, instead of0.07 g of Darocure-1173 in Example 3.

Example 23 Production of the Photopolymerizable Composition for Sealinga Light emitting Element of the Present Invention

The photopolymerizable composition for sealing the light emittingelement was produced in the same manner as in Example 1, except that0.20 g (0.20 weight % to the total weight of the polymerizable compound)of 2-hydroxy-2-methyl-1-phenyl propane-1-on (Darocure-1173) as aphotopolymerization initiator was used, instead of 0.07 g of diphenyl(2,4,6-trimethyl benzoyl) phosphine oxide in Example 4.

Example 24 Sealing of a Light Emitting Element by the PhotopolymerizableComposition of the Present Invention

An optical semiconductor equipment having a light emitting diode (LED)in a structure as illustrated in FIG. 1 was manufactured by sealing alight emitting element using the photopolymerizable composition producedin Example 22. Namely, the photopolymerizable composition for sealing alight emitting element manufactured in Example 22 using a well washedglass Pasteur's pipette was suspended at a portion of the light emittingelement so that an interface with the air is on the dome. Using a metalhalide lamp (120 W/cm), ultraviolet rays were irradiated on this portionfor 2 minutes, the composition was polymerized and cured, then furtherheat-treated at 80° C. for an hour in an inert gas oven, thus forming asealing resin layer. The light transmittance of the cured product (resinlayer) was good and the refractive index (nd) at 25° C. was 1.598.

FIG. 1 is a cross sectional view of the optical semiconductor equipmentof the present invention. In FIG. 1, 1 indicates a sealing resin layerthat is formed using the sealing material of the present invention.

Example 25 Sealing of a Light Emitting Element by the PhotopolymerizableComposition of the Present Invention

An optical semiconductor equipment having a light emitting diode (LED)in a structure as illustrated FIG. 1 was manufactured by performing thesame manipulation as in Example 24 and sealing a light emitting elementusing the photopolymerizable composition produced in Example 23. Thelight transmittance of the cured product (resin layer) was good and therefractive index (nd) at 25° C. was 1.600.

FIG. 1 is a cross sectional view of the optical semiconductor equipmentof the present invention. In FIG. 1, 1 indicates a sealing resin layerthat is formed using the sealing material of the present invention.

Example 26 Sealing of a Light Emitting Element by the PhotopolymerizableComposition of the Present Invention

An optical semiconductor equipment having a light emitting diode (LED)in a structure as illustrated in FIG. 2 was manufactured in the samemanner as in Example 24. Namely, a sealing resin layer 1 was formedusing the photopolymerizable composition for sealing material of a lightemitting element produced in Example 22 and a sealing resin layer 2 wasfurther formed using a known bisphenol A type epoxy resin on the outerside thereof.

FIG. 2 is a cross sectional view of the optical semiconductor equipmentof the present invention. In FIG. 2, 2-1 indicates a sealing resin layerthat is formed using the sealing material of the present invention.

Comparative Example

The optical semiconductor equipment was manufactured using a knownbisphenol A type epoxy resin sealing material and sealing a lightemitting diode according to known polymerization conditions instead ofthe composition for a sealing material of a light emitting element ofthe present invention.

Light extraction efficiency of the optical semiconductor equipment ofthe present invention manufactured in Examples 24 to 26 was better thanthe case where the conventional known epoxy resin type sealing materialwas used.

Furthermore, the sealing material of the light emitting element of thepresent invention is a useful material in which transparency and heatresistance are good, mechanical intensity such as flexural strength ispractically sufficient, deterioration of the permeability by light islow.

The photopolymerizable composition of the present invention enablespolymerization and forming within a short period of time withoutaccompanying depreciation of coloring and transparency, opticaldistortion upon photopolymerization, thus enabling production of opticalresins and optical parts in which optical properties (high refractiveindex and high Abbe number), thermal properties and mechanicalproperties are good.

INDUSTRIAL APPLICABILITY

The photopolymerizable composition of the present invention enablespolymerization and forming within a short period of time withoutaccompanying depreciation of coloring and transparency, opticaldistortion upon photopolymerization, and can be used as an optical resinand optical parts in which optical properties (high refractive index andhigh Abbe number), thermal properties and mechanical properties aregood.

1. A photopolymerizable composition comprising a polymerizable compoundand a photopolymerization initiator, wherein the polymerizable compoundcomprises (a) a bifunctional (meth)acrylic acid (thio)ester compoundcontaining a sulfur atom in the molecule and (b) at least one of a(meth)acrylic acid ester compound represented by the following generalformula (1) and a bifunctional (meth)acrylic acid ester compound havinga urethane linkage:

wherein R₁ and R₂ are each independently a hydrogen atom or a methylgroup; R₃ and R₄ are each independently an alkyl group, an aralkylgroup, an aryl group or a halogen atom; m and n are each an integer of 0to 2; X₁ is an alkylidene group having 1 to 3 carbon atoms; and Y₁ andY₂ are each independently a poly(oxyalkylene) group with the provisothat at least one of Y₁ and Y₂ is a poly(oxyalkylene) group having ahydroxy group.
 2. A photopolymerizable composition comprising apolymerizable compound and a photopolymerization initiator, wherein thepolymerizable compound comprises (a) a bifunctional (meth)acrylic acid(thio)ester compound containing a sulfur atom in the molecule and (b) a(meth)acrylic acid ester compound represented by the following generalformula (1):

wherein R₁ and R₂ are each independently a hydrogen atom or a methylgroup; R₃ and R₄ are each independently an alkyl group, an aralkylgroup, an aryl group or a halogen atom; m and n are each an integer of 0to 2; X₁ is an alkylidene group having 1 to 3 carbon atoms; and Y₁ andY₂ are each independently a poly(oxyalkylene) group having a hydroxygroup.
 3. The photopolymerizable composition according to claim 1,wherein the polymerizable compound further comprises (c) polythiols. 4.The photopolymerizable composition according to claim 3, wherein (a) abifunctional (meth)acrylic acid (thio)ester compound containing a sulfuratom in the molecule is represented by the following general formula(2):

wherein R₅ is a chain alkylene group having at least one or more sulfuratoms in the group or R₅ is the following linking group; R₆ and R₇ areeach independently a hydrogen atom or an alkyl group; and Z₁ and Z₂ areeach independently an oxygen atom or a sulfur atom with the proviso thatone of Z₁ and Z₂ is a sulfur atom in case R₅ is the following linkinggroup:

wherein R₁₂ and R₁₃ are each independently an alkyl group, an aralkylgroup, an aryl group or a halogen atom; and q and r are each an integerof 0 to
 2. 5. The composition according to claim 4, wherein Y₁ and Y₂groups in the general formula (1) are the following group:


6. A cured product obtained by polymerizing the photopolymerizablecomposition as described in claim
 5. 7. Optical parts made of the curedproduct as described in claim
 6. 8. A light emitting element made bysealing with the cured product as described in claim
 6. 9. Thephotopolymerizable composition according to claim 1, wherein (a) abifunctional (meth)acrylic acid (thio)ester compound containing a sulfuratom in the molecule is represented by the following general formula(2):

wherein R₅ is a chain alkylene group having one or more sulfur atoms inthe group or R₅ is the following linking group; R₆ and R₇ are eachindependently a hydrogen atom or an alkyl group; and Z₁ and Z₂ are eachindependently an oxygen atom or a sulfur atom with the proviso that oneof Z₁ and Z₂ is a sulfur atom in case R₅ is the following linking group:

wherein R₁₂ and R₁₃ are each independently an alkyl group, an aralkylgroup, an aryl group or a halogen atom; and q and r are each an integerof 0 to
 2. 10. The composition according to claim 1, wherein Y₁ and Y₂groups in the general formula (1) are the following group:


11. A cured product obtained by polymerizing the photopolymerizablecomposition as described in claim
 1. 12. Optical parts made of the curedproduct as described in claim
 11. 13. A light emitting element made bysealing with the cured product as described in claim
 11. 14. Thephotopolymerizable composition according to claim 2, wherein thepolymerizable compound further comprises (c) polythiols.
 15. Thephotopolymerizable composition according to claim 14, wherein (a) abifunctional (meth)acrylic acid (thio)ester compound containing a sulfuratom in the molecule is represented by the following general formula(2):

wherein R₅ is a chain alkylene group having one or more sulfur atoms inthe group or R₅ is the following linking group; R₆ and R₇ are eachindependently a hydrogen atom or an alkyl group; and Z₁ and Z₂ are eachindependently an oxygen atom or a sulfur atom with the proviso that oneof Z₁ and Z₂ is a sulfur atom in case R₅ is the following linking group:

wherein R₁₂ and R₁₃ are each independently an alkyl group, an aralkylgroup, an aryl group or a halogen atom; and q and r are each an integerof 0 to
 2. 16. The composition according to claim 15, wherein Y₁ and Y₂groups in the general formula (1) are the following group:


17. A cured product obtained by polymerizing the photopolymerizablecomposition as described in claim
 16. 18. Optical parts made of thecured product as described in claim
 17. 19. A light emitting elementmade by sealing with the cured product as described in claim
 17. 20. Thephotopolymerizable composition according to claim 2, wherein (a) abifunctional (meth)acrylic acid (thio)ester compound containing a sulfuratom in the molecule is represented by the following general formula(2):

wherein R₅ is a chain alkylene group having one or more sulfur atoms inthe group or R₅ is the following linking group; R₆ and R₇ are eachindependently a hydrogen atom or an alkyl group; and Z₁ and Z₂ are eachindependently an oxygen atom or a sulfur atom with the proviso that oneof Z₁ and Z₂ is a sulfur atom in case R₅ is the following linking group:

wherein R₁₂ and R₁₃ are each independently an alkyl group, an aralkylgroup, an aryl group or a halogen atom; and q and r are each an integerof 0 to
 2. 21. The composition according to claim 2, wherein Y₁ and Y₂groups in the general formula (1) are the following group:


22. A cured product obtained by polymerizing the photopolymerizablecomposition as described in claim
 2. 23. Optical parts made of the curedproduct as described in claim
 22. 24. A light emitting element made bysealing with the cured product as described in claim 22.